1. Technical Field
The present invention relates to chromatic aberration detection and correction, and image processing using the detection and correction.
2. Description of the Related Art
In image devices using lenses such as cameras, a variety of aberrations occur due to a unique property of the lens. Typical examples of the aberrations include Seidel's 5 aberrations, which are monochromatic aberrations. These aberrations include a spherical aberration, a coma aberration, an astigmatism aberration, a distortion aberration, and a curvature distortion, which are based on a spherical surface of lens.
Also, there are chromatic aberration in which false colors are generated due to a different refractive index for a lens according to a wavelength of light. Chromatic aberration refers to a phenomenon in which a color fringe is formed around a boundary of an image as light passing through a lens is divided due to a physical property of a different refractive index of the lens according to a wavelength of light, such that the image is not formed on the same portion of a sensor. The chromatic aberration phenomenon may be classified as a longitudinal chromatic aberration in which a color blurs due to a different focal distance on an optical axis according to a wavelength of light, or a lateral chromatic aberration phenomenon in which a different magnification of an image appears according to a distance from an optical axis.
Chromatic aberration phenomena occur in all image devices using lenses. To reduce the chromatic aberration phenomenon, a lens has been formed of a special material. This increases the price of the lens, which is not applicable to small cameras having non-detachable lenses. Alternatively, methods of correcting such a distortion through image processing, mainly using additional information such as camera settings upon photographing, have been developed. Automatic correction methods for correcting chromatic aberrations using only image information without such additional information have also been studied.
Recently, high resolution cameras have been developed for high image quality. The high resolution cameras suffer from chromatic aberration due to smaller pixels of a sensor. To reduce the chromatic aberration phenomenon, a lens has been formed of a special material. This increases the price of the lens, which is not applicable to small cameras having non-detachable lenses.
Chromatic aberration correction schemes using image processing have been studied to correct chromatic aberrations in small cameras. Mainly, schemes of calculating a magnification difference of an image for each color with reference to a center point of a distortion and warping the image to correct a lateral chromatic aberration have been studied. Also, schemes of designating all specific colors near bright areas, such as a purple fringe, as having a chromatic aberration and then correcting the chromatic aberration using adjacent signals have been studied.
Most conventional schemes are focused on detection and correction of a lateral chromatic aberration that can be easily analyzed and corrected. The schemes require information on camera settings upon photographing images or additional information such as photographed images for a certain test pattern. Schemes requiring no additional information have different correction performance according to accuracy of estimation of a center point of a distortion upon correcting a lateral chromatic aberration. In addition, since the lateral chromatic aberration and the longitudinal chromatic aberration occur simultaneously upon photographing images, a sufficient correction result cannot be obtained due to presence of the longitudinal chromatic aberration even when the lateral chromatic aberration is accurately corrected.
A phenomenon in which false colors are generated in an edge of an image due to a different point image distribution according to a wavelength of light is called purple fringe. Since the scheme of designating all specific colors near a bright area such as a purple fringe as having a chromatic aberration and correcting the chromatic aberration using adjacent signals is used to detect and correct distortions of the specific colors, it can effectively remove the specific colors such as the purple fringe, but cannot detect all colors with chromatic aberration. Further, false matches and mismatching of areas may cause a severe blurring phenomenon.